Azure Active Directory API始终显示禁止消息

我是使用Azure Active Directory实施的初学者。我有一个带有Azure Active Directory保护的WEB API（.net核心）。我正在尝试通过邮递员使用我的WEB API，我知道它需要Auth2令牌才能使用Web API。我已经按照此文档链接生成了auth2令牌。

生成Auth2令牌后，在标头中添加auth2令牌，例如，Authorization: Bearer e....但结果始终显示如下图所示。

我确定我会在“ API权限”部分中提供所需的权限，并且在Azure Portal中“权限类型”是“委派的权限”。

请参阅我的启动课程：

public class Startup
{
    public Startup(IConfiguration configuration)
    {
        Configuration = configuration;
    }

    public IConfiguration Configuration { get; }

    public void ConfigureServices(IServiceCollection services)
    {
        services.AddMvc(o =>
        {
            o.Filters.Add(new AuthorizeFilter("default"));
        }).SetCompatibilityVersion(CompatibilityVersion.Version_2_1);

        services.AddAuthorization(o =>
        {
            o.AddPolicy("default", policy =>
            {
                // Require the basic "Access app-name" claim by default
                policy.RequireClaim(DotNetCoreApiSample.Authorization.Constants.ScopeClaimType, "user_impersonation");
            });
        });

        services
            .AddAuthentication(o =>
            {
                o.DefaultScheme = JwtBearerDefaults.AuthenticationScheme;
            })
            .AddJwtBearer(o =>
            {
                o.Authority = Configuration["Authentication:Authority"];
                o.TokenValidationParameters = new Microsoft.IdentityModel.Tokens.TokenValidationParameters
                {
                    // Both App ID URI and client id are valid audiences in the access token
                    ValidAudiences = new List<string>
                    {
                    Configuration["Authentication:AppIdUri"],
                    Configuration["Authentication:ClientId"]
                    }
                };
            });
        // Add claims transformation to split the scope claim value
        services.AddSingleton<IClaimsTransformation, AzureAdScopeClaimTransformation>();
    }

    public void Configure(IApplicationBuilder app, IHostingEnvironment env)
    {
        if (env.IsDevelopment())
        {
            app.UseDeveloperExceptionPage();
        }

        // Very important that this is before MVC (or anything that will require authentication)
        app.UseAuthentication();

        app.UseMvc();
    }
}